1. Field of the Invention
The present invention relates to an apparatus for inspecting an alignment film and, more particularly, to an apparatus for inspecting an alignment film comprising a rubbing steam inspecting unit for performing inspecting on alignment films to check whether they are defective, and a method for fabricating a liquid crystal display (LCD) device using the same.
2. Description of the Related Art
Recently, as the demand for information displays has increased, especially for the use in portable (mobile) information devices, research and development of light thin flat panel displays (FPD), which can replace the CRT (Cathode Ray Tube), the existing display device, have increased.
Among FPDs, LCDs, devices for displaying images by using optical anisotropy of liquid crystal, exhibit excellent resolution and color and picture quality, so LCDs are widely used in notebook computers, desktop monitors or the like.
In general, the LCD device is a display device in which a data signal according to image information is separately supplied to liquid crystal cells arrange din a matrix form to control optical transmittance of the liquid crystal cells to thereby display a desired image.
The LCD device will now be described with reference to FIG. 1.
FIG. 1 is an exploded perspective view illustrating the structure of a related art LCD device.
As illustrated, the LCD device comprises a color filter substrate 5, a first substrate, an array substrate 10, a second substrate, and a liquid crystal layer 40 formed between the color filter substrate 5 and the array substrate 10.
The color filter substrate 5 comprises a color filter (C) comprised of red (R), green (G) and blue (B) sub-color filters 7, a black matrix 6 separating the sub-color filters (C) and blocking light transmitted through the liquid crystal layer 40, and a transparent common electrode 8 applying a voltage to the liquid crystal layer 40.
On the array substrate 10, there are formed gate lines 16 and data lines 17 arranged vertically and horizontally to define pixel regions (P). A thin film transistor (TFT), a switching device, is formed at the crossing of the gate line 16, and a pixel electrode 18 is formed at each pixel region (P).
The pixel region (P) is a sub-pixel corresponding to a single sub-color filter 7, and a color image is obtained by combining three types of red, green and blue colors. Namely, the three red, green and blue sub-pixels make one pixel, and the TFT (T) is connected to the red, green and blue sub-pixels.
An alignment film (not illustrated) for aligning liquid crystal molecules of the liquid crystal layer is formed on the color filter substrate 5 and the array substrate 10.
FIG. 2 illustrates a method for forming the alignment film using a roll printing method.
As illustrated, generally, an alignment film is formed by using a printing method using a plurality of rolls. Namely, an alignment solution 24 is supplied between a cylindrical anylox roll 22 and a doctor roll 23 and when the anylox roll 22 and the doctor roll 23 are rotated, the alignment solution 24 is uniformly coated entirely on the anylox roll 22. In this case, the alignment solution 24 is supplied by a dispenser 1 in an injector type.
The anylox roll 22 is rotated in contact with a printing roll 24 with a rubber plate 25 attached on a certain region of its surface, and the alignment solution 24 on the anylox roll 22 is transferred to the rubber plate 25. The rubber plate 25 corresponds to a substrate 26 on which the alignment solution 24 is to be coated, and has a master pattern to allow the alignment film to be selectively printed on the substrate.
As a printing table 27 with the substrate 26 loaded thereon is moved in contact with the printing roll 24, the alignment solution 24 which has been transferred to the rubber plate 25 is re-transferred onto the substrate 26 to thereby form an alignment film. Generally, the alignment film has the thickness of 500˜1000 Å, and in this respect, even a thickness difference of about 100 Å can cause a defect such as a blot (spot) on a screen of the LCD device according to the non-uniformed alignment, so uniformly coating of the alignment film is a critical factor for determining characteristics of the screen.
Next, with the alignment film formed on the substrate, the alignment film is rubbed to arrange liquid crystals in a certain direction to form valleys in a certain direction.
FIG. 3 is a perspective view illustrating a related art rubbing process.
As illustrated, the alignment film 21 is rubbed to form the recesses 36 on the surface thereof. The rubbing process refers to rubbing the surface of the alignment film 21 in a certain direction by using a roller 30 with a rubbing cloth 35 wound thereon.
When the surface of the alignment film 21 is rubbed, it has fine recesses 36.
For the rubbing cloth 35, a soft cloth is used. The rubbing equipment including the roller 30 is relatively simple. The basic part for setting conditions for the rubbing process is setting a rubbing condition with a suitable strength and applying a uniform rubbing strength on a large area.
If the rubbing is not uniform, an alignment degree of liquid crystal molecules will not be spatially uniform, causing a defect that optical characteristics are different at a certain portion.
Checking for a defective alignment after rubbing is generally performed such that the rubbing state of the alignment 21 is checked with the naked eye by reflecting light on the surface of the substrate 26, or liquid crystal is dropped on the alignment film 21, the upper and lower substrates are allowed to overlap and a resulting color change or a light and shade difference is checked with the naked eye.
However, the method for checking the alignment film with the naked eye by using the light reflection is unreliable, and the method for using liquid crystal has a degraded process yield because a large amount of liquid crystal is consumed and the substrate used for the checking is to be discarded.